ANTIMICROBIAL EFFECTS OF SELECTED HERBAL EXTRACTS ON MULTI-DRUG RESISTANT ...

13 Pages·2012·0.17 MB·English

ANTIMICROBIAL EFFECTS OF SELECTED HERBAL EXTRACTS ON MULTI-DRUG RESISTANT GRAM-NEGATIVE
BACTERIAL STRAINS

M. M. Njire1, N. L.M. Budambula2 and J. N. Kiiru3
1,2Department of Botany, Jomo Kenyatta University of Agriculture and Technology, Nairobi Kenya
3Centre for Microbiology Research, Kenya Medical Research Institute, Nairobi Kenya
E-mail: [email protected]

Abstract
The rise in antibiotic resistance has resulted in a decreasing number of fully active antimicrobial agents
available to treat infections by multi-drug resistant (MDR) bacteria. This has necessitated a search for new
antimicrobial agents. Herbal remedies may offer novel treatment options which elicit little or no transferred
resistance if used in optimal concentrations. This study evaluated the antimicrobial properties of ten plants
traditionally used as herbal remedies against 27 multi-drug resistant Gram-negative bacterial isolates. The
herbal extracts were obtained through extraction with organic (methanol) and inorganic (water) solvents.
Susceptibility of the test strains to conventional antibiotics was determined by the disc diffusion technique.
Determination of the Minimum Inhibitory Concentrations (MIC) and the sub-lethal concentrations of the most
effective extracts against the MDR strains was done by broth inoculation followed by colony count method.
The effect of sub-lethal extract concentrations was done by a method modified from McMahon et al. (2007).
Out of the ten plants, only Warbugia ugandensis was active against the MDR strains and its efficacy was
significantly different from that of other plant extracts such as Terminalia brownii, Azaridachta indica,
Clausena anisata and Strychnos henningsii (p<0.001). The root and bark methanol extracts from W.
ugandensis were the most effective with an MIC of 42 µg/ml. Susceptibility of test strains to conventional
antibiotics was not significantly different before and after habituation to sub-optimal extract concentration
(p>0.005). Methanol extracts from the root and bark of W. ugandensis provide potential sources of effective
antimicrobial compounds for further development of alternative safe antimicrobial products in form of
chemotherapeutic agents or antiseptics. The optimization and standardization of operation procedures and
methods of analysing the efficacy of herbal extracts demands serious consideration.

Key words: Multi-drug resistant (MDR) bacteria, Minimum Inhibitory Concentrations (MICs), Sub-Lethal
Concentration (SLC)
131
1.0 Introduction
Antimicrobial agents have substantially reduced the threat posed by infectious diseases over a period of time
since their discovery in the 1940s (Lewis and Ausubel, 2006). However, the escalation of multidrug resistance
in bacteria in recent years has seriously jeopardized these gains. This has gained worldwide attention due to
the high impact on public health. Increased usage of antimicrobial agents to treat bacterial infections has lead
to the emergence of multi drug resistant (MDR) strains (Bonnet, 2004). Such strains are resistant to first line of
treatments and also the more expensive second and third-line antibiotics. The high cost of such replacement
drugs and the toxicological effects are prohibitive and are out of reach for many Kenyans. Furthermore, newer
antimicrobials are losing their effectivity fast due to transfer of resistance markers from resistant to
susceptible bacterial strains. This scenario has necessitated a search for new antimicrobial substances from
other sources especially plants, which produce diverse chemical compounds with different biological activities
(Lewis and Ausubel, 2006).

Plants form an integral part of life in many indigenous African communities as a readily and cheaply available
alternative to allopathic medicines. Such plants have been found to cure urinary tract infections,
gastrointestinal disorders, respiratory diseases and cutaneous infections (Somchit et al., 2003), caused by
bacteria often known to resist various classes of conventional antibiotics. Due to either limited availability or
affordability of pharmaceutical medicines about 80% of the rural population in Sub-Saharan Africa (SSA)
depends on traditional herbal remedies for primary health care (PHC) (WHO, 2002). Therefore, provision of
safe and effective traditional medicines could become a critical tool to increase access to health care (WHO,
2002). It is expected that plant extracts exhibiting effective inhibition to microbial growth may provide less
toxic, cheaper and more affordable alternatives for infection management. Moreover, the more efficient
inhibition and lysis of bacteria resulting from the synergistic reactions of the active ingredients in plant extracts
decreases the risk of progressively increasing antibiotic resistance (Miyasaki et al, 2010).

2.0 Materials and Methods
2.1 Test Strains
The test strains were selected from each of the following species; E. coli, Klebsiella pneumoniae, Pseudomonas
aeruginosa, and Salmonella typhi, and their susceptibility patterns to different classes of antibiotics was
determined. All the isolates had combined resistance to at least; two quinolones, two or more cephalosporins
belonging to different classes, two aminoglycosides, one or two tetracyclines, and to one or more β- lactam/β-
lactamase inhibitor.

2.2 Preparation of Plant Materials
The ten plants investigated in the study are those traditionally used for the treatment of bacterial infections by
Kenyan communities (Table 1). The leaf, bark and root samples were harvested, packed in clean sterile manila
papers, labelled with a voucher specimen and transported to the laboratory for analysis. The materials were
oven-dried at 25°C and weighed every day until a constant weight was attained after which they were chopped
and ground to fine powder using a motor grinder. The herbal extracts were obtained through extraction with
organic (methanol) and inorganic (water) solvents.

2.3 Extraction of Plant Extracts
Warm water extraction was done to simulate the traditional decoction method of preparing herbal
preparations. Sixty (60) g of the ground powder was soaked in 300 ml sterile distilled and deionised water at
50ºC for 1 hr, placed in an orbital shaker at 100 rpm for 24 h at 25ºC. The resulting elute was membrane-
filtered and lyophilized into granules (LyoBeta range, Telstar, UK). Stock solutions were prepared by dissolving
0.4 g of the granules in 20 ml of deionised sterile distilled water while another set of a similar amount of
preparations was dissolved in TE buffer (pH 8), and stored at -20ºC until further use.

Organic extraction was done using methanol. Sixty (60) g of the ground powder was soaked for 72 hr in a
beaker containing 300 ml of methanol (Analytical Grade, 99.9%, Sigma-Aldrich, UK) and placed in an orbital
shaker (Basic Model, Cole-Parmer, UK) at 100 rpm for 72 h at 25ºC. The resulting extracts were membrane
filtered on a whatman paper number 1 then the filtrate concentrated at 50ºC using a vacuum rotary
evaporator (Basic Model, Buchi, UK). In order to evaporate the methanol used as the extraction solvent, the
concentrates were oven-dried at 25°C until a constant weight was attained. Excess methanol was evaporated
by further air-drying the paste at 25°C until a constant weight was attained. Stock solutions of the methanol-
free paste were prepared by dissolving 0.4 g in 20 ml of deionised sterile distilled water. Another preparation
132
was dissolved in TE buffer at pH 8 as an alternative diluent. The preparations were stored at -20ºC until further
use.

2.4 Pre-Screening of the Herbal Extracts for Antimicrobial Activity against Test Strain
Preliminary screening of the extracts for antimicrobial effect was done using E. coli J53 as the test organism.
This strain has a defined genetic background and is susceptible to all conventional antibiotics except Sodium
azide. A confluent lawn of the bacteria was prepared from a 0.5 MacFarland equivalent (approximately 106
CFU/ml) and placed in an incubator to dry after which 0.5 μl of the test extracts were point inoculated using a
micropipette (Eppendorf, Hamburg, Germany). Other sets of preparations were made in a similar way and
used for testing the efficacy at each of the following titres: 1 μl, 5 μl, 10 μl, 30 μl, 80 μl or 100 μl. Extract-free
sterile distilled water and TE buffer (the diluents used for making the stock solutions of the test extracts), were
inoculated in another set of these plates and used as negative controls. The plates were allowed to stand for at
least 1 hr at room temperature for the extracts to diffuse at the point of inoculation before incubation at 37°C
for 8 h. Observation of a clear zone on bacterial lawn at the point of inoculation of the extract was interpreted
as evidence of inhibition of bacterial growth. The diameter of these zones were measured and recorded to the
nearest size mm. The plants whose extracts exhibited an inhibition zone > 20 mm were selected for further
testing of clinical isolates.
2.5 Determination of MICs and the Sub-Lethal Concentrations of the Herbal Extracts
Duplicate tubes containing 2 ml MH broth were prepared. To one set of these tubes, separate titres of the
extract in the range of 5µl-120ul were added to separate tubes before a uniform inoculum of 106 CFU/ml of
the test isolates was added to each tube. Negative controls were set in a similar way but using distilled water
or TE buffer instead of the extracts. The preparations were incubated for 8 h at 37ºC with continous shaking at
100 rpm in an orbital shaker. The tubes were removed from the shakers and arranged sequentially with
increasing concentration of the herbal extract titre added. The tubes were then assessed for evidence of
bacteria growth by physical examination before streaking 1 µl of the preparations on MacConkey plates. The
plates were then incubated for 8 hr and the colonies counts determined. The tube containing the lowest
concentration at which no colonies were observed was identified and calculations done to determine the
appropriate concentration of the herbal extract added. This concentration was identified as the MIC. The tube
containing the preparation at which the last visible growth was observed was identified as the highest amount
of extract that does not inhibit bacterial growth. This concentration was therefore identified as the highest
sub-lethal concentration of the extract. This sub-lethal concentration was used as the reference concentration
in the habituation experiment discussed in section 2.6 below.

2.6 Habituation to Sub-lethal Concentrations (Modified from McMahon et al., 2007)
Two sets of duplicate tubes containing 2 ml MH broth were prepared. The sub-lethal concentration of an
extract was added and inoculated with approximately 106 CFU/ml bacterial cells of the clinical isolates or
controls ATCC E. coli strains 25922 and J53. Negative controls were prepared using similar sets of bacterial
preparations but instead of the extracts, deionised sterile distilled water or TE buffer (pH 8) was used as
blanks. All preparations were incubated for 72 h at 37ºC with shaking at 100 rpm after which colony counts
were determined on MacConkey agar.

3.0 Results
3.1 Susceptibility Profiles of Test Strains to Conventional Antibiotics
All the 27 test isolates had combined resistance to at least; two quinolones, two or more cephalosporins, two
aminoglycosides, tetracyclines, trimethoprim, and to at least one or more β- lactam/β- lactamase inhibitor. All
isolates were resistant to ampicillin, 26 resistant to augmentin and only 8 isolates were resistant to cefoxitin
(Table 2).

3.2 Pre-Screening of the Herbal Extracts for Antimicrobial Activity
The extracts from the 10 plants exhibited antibacterial effect and this depended on the plant species, part of
the plant used, method of extraction and the volume of extract used (Table 3). Methanol extracts of W.
ugandensis had a high antimicrobial effect even at titres as low as 0.5 µl from the 1 ug/ml of the plant extract
preparation. There was a strong correlation between the amount of titre used and the zone of inhibition.
Plants whose extracts of 100 µl produced an inhibition zone of greater than 24 mm were selected for further
133
testing using the clinical strains and their MICs determined. The plants whose extracts met this criterion were:
W. ugandensis; T. brownii; A. indica; C. anisata and S. henningsii (Table 3).

3.3 Characterization of Plants with Inhibitory Effect
The five plants whose extracts produced an inhibition zone ≥24 mm at 100 µl were further tested using clinical
Gram-negative isolates. Although extracts from these plants had been tested to give inhibitory effect on E. coli
J53, only methanol extracts from the root and bark of W. ugandensis were inhibitory to the MDR strains. Mean
colony counts were obtained by averaging the colony counts for the duplicate sets at 100 µl of the extracts and
their standard error (SE) obtained (Figure 1). Inhibition of the other clinical isolates was similar to that of E.
coli isolate, E .
1

3.4 Inhibitory Characteristics of W. ugandensis
Figure 2 indicates a comparison of inhibitory characteristics of different parts of W.ugandensis. Methanolic
extracts from the bark of W. ugandensis exhibited better inhibitory properties than those obtained using water
extraction (p<0.001). Similarly, the root extracts obtained using methanol from this plant were more effective
than those obtained using water extraction method (p < 0.01), However, there were no significant differences
in the methanolic and water extracts from the leaf (p=0.298). The inhibition characteristics of root and bark
extracts obtained using methanol were not significantly different (t-test, p = 0.908)
Figure 3 shows the inhibition trend, MIC and sublethal concentrations of extracts from W. ugandensis. There
was a gradual decrease in the number of colonies as the amount of titre (root and bark methanol extracts)
increased. The colony counts from all other non-effective plants were not significantly different from those of
the negative controls (P > 0.05) indicating that there was no inhibition. Colony counts decreased as methanol
extract titres for the root and bark increased. Mean colony represents average colony counts for the duplicate
sets at 100 µl of W. ugandensis extracts against a clinical K. pneumoniae isolate, K, and their standard errors
1
(SE) (Figure 2). Inhibition was similar for the other clinical isolates. There were no colonies at titres > 42 µl for
the bark and root extracts. Therefore, the MIC for W. ugandensis methanolic root and bark extracts was 42.5
µg/ml. Consequently, the highest sublethal extract concentration for both the root and bark was thus 32.5
µg/ml (Figure 2).
Table 4 indicates mean inhibition zones of 15 conventional antibiotics against a S. typhi isolate, S3, before and
after exposure to sub-optimal concentration (32.0 µg/ml) of W. ugandensis methanolic root extract. All the
other clinical isolates had a similar trend. Bacterial strains exposed to a sub-optimum concentration of
W.ugandensis methanolic extracts from the root and bark exhibited no significant differences in their
antibiotic susceptibility profiles before and after exposure (t-test, p > 0.005).

4.0 Discussion
This study reports efficiency of extracts from W. ugandensis among the 27 Gram-negative bacterial isolates
analysed. Varied antibacterial activity between the root/bark and leaf extracts observed are attributed to the
different secondary metabolites found in these plant parts. The fact that the study also reports resistance by
these isolates to different groups of antibiotics show that our extracts are a potential to offering effective, less
expensive treatment options to diseases caused by these Gram-negative MDR strains. Characterization of
specific anti-bacterial substances from the root and bark extracts will be an important step for potential
development of novel anti-microbial agents against related strains.

On the basis of zones of inhibition, our results also revealed that extracts from five plants inhibited the growth
of E. coli strain J53 indicating that such plants have a potential as anti-microbial agents and may require
further testing for drug development. Other studies on medicinal plants (Thakurta et al., 2009; Osuga et al.,
2006) have also realized a potential for these plants in the control of bacterial strains that exhibit resistance to
conventional antibiotics.

The finding in our study that the MDR strains were only inhibited by methanol preparations from root and bark
of W. ugandensis indicate that the extracts provide potential sources of effective anti-microbial compounds for
further development of alternative safe anti-microbial products in form of chemotherapeutic agents or
antiseptics. W. ugandensis has been used traditionally to treat bacterial infections and previous studies have
reported its anti-bacterial activity. Crude extracts and purified compounds from W. ugandensis have been
134
reported to be effective against Mycobacterium tuberculosis, E. coli and Vibrio cholerae (Mbwambo et al.,
2009). Wube et al. (2005), reported antimycobacterial activity of dichloromethane stem bark extracts against
M. aurum, M. fortuitum, M. phlei and M. Smegmatis. The active constituents showed MIC values ranging from
4 to128 µg/ml compared to the antibiotic drugs ethambutol (MIC range from 0.5 to 8 µg/ml) and isoniazid
(MIC range from 1 to 4 µg/ml). This closely corroborate with the results of our study in which methanolic root
and bark extracts showed strong anti-bacterial activity with an MIC value of 42.5 µg/ml. Such an MIC indicates
antibacterial potential comparable to that of conventional antibiotics like gentamicin (Tadeg et al., 2005).

Phytochemical investigations of this plant have identified drimane-type sesquiterpenoids as the main active
components. Published work (e.g. Brooks and Draffan, 1969; Wube et al., 2005), has reported the presence of
sesquiterpenoids in heartwood (e.g. ugandensolide, ugandesidial, warburgin and warburgiadione) and stem
bark (e.g. muzigadiolide, deacetylugandensolide, cinnamolide, mukaadial, ugandensidial, muzigadial and
waburganal). Flavonol glycosides and monoterpenes have been detected from the leaves of this plant
(Manguro et al. 2003). Based on this information, this study did not carry out any phytochemical analysis but
rather screened the crude extracts for their antimicrobial potential.
It is known that, in general, plant extracts are more effective against Gram-positive than Gram-negative
bacteria (Suffredini et al., 2006). However, our study showed that the Gram-negative organisms used were
sensitive to the plant extracts even at low MICs. Therefore, these findings further support the idea that W.
ugandensis may be an important source of compounds with broad-spectrum anti-microbial properties.
Results obtained with extracts from other plants including T. brownii, A. indica, C. anisata, S. henningsii, Z.
chalybeum, A. remota, T. indica, R. communis and A. Secundiflora were significant in their own accord. From
these results we note that although they are traditionally used in management of bacterial diseases, not all
prescribed anti-bacterial medicinal plants may be effective against multi-drug resistant Gram-negative
pathogens. The results may also suggest that the resistance observed for other plant extracts may partially be
due to efflux pumps in the bacteria. Many efflux systems are multidrug transporters capable of expelling a
wide spectrum of structurally unrelated drugs and anti-microbials, thus contributing significantly to
bacterial multi-drug resistance (Veen and Konings, 2007).
The contrasting results of this study with those published by other investigators on anti-microbial activities of
other plant extracts apart from W. ugandensis could be due to methodological discrepancy. For instance,
Thakurt et al., (2007) reported significant antibacterial activity of Azadirachta indica leaf extracts against multi-
drug-resistant Vibrio cholerae, while Tajamul et al. (2010) reported good anti-bacterial activity of Ricinus
communis against pathogenic bacterial strains like K. pneumoniae and E. coli. This could be attributed to
differences in bioassay techniques used and diluents used for extraction and elution. Thakurt et al. (2007) and
Tajamul et al. (2010) used the disc diffusion technique to assay the anti-microbial activity of the plant extracts.
Such standard anti-microbial susceptibility testing methods like the agar diffusion and Kirby-Bauer may result
to misinterpretation of results especially for extracts with low anti-microbial activity or in cases where the
active ingredient(s) may irreversibly bind to the paper discs (Das et al., 2010). To overcome these drawbacks,
the anti-microbial activity of the crude plant extracts was detected by performing viable counting following
direct inoculation. This method allows for maximum action by the extract on the bacterial cells hence
generating more reliable data. Besides the methodological approaches used by various investigators, the
contrasting results could also be attributed to the locality of plant species, storage conditions, test strains
used, and lack of appropriate positive and negative controls in some of these studies.
However, this study does not rule out the potential of such plants as agents for the treatment of infections
caused by other agents. Besides, the plants may be effective while in combination with other medicinal plants
or in combination with conventional antibiotics but further research to support this opinion is needed.
Furthermore, some plants found not to have inhibitory effects in vitro may undergo enzymatical processing to
make them effective in vivo. Others may become more potent in the presence of other components involved
in immune response (Gonzalez-Lamothe et al., 2009).
In a previous study by McMahon et al. (2007), the continued use of tea tree oil as a herbal remedy in sub-
optimal concentrations was shown to elicit the emergence of resistance to conventional antibiotics. The
current study shows otherwise in which exposure of the MDR strains to sub-optimal extract concentration of
135
W. ugandensis extracts had no effect on their susceptibility to conventional antibiotics and conjugative
efficiency. Very little has been done to screen other herbal extracts for similar effects and it is not known if
such herbal-elicited antibiotic resistance is transferable via conjugation or whether the presence of herbal
agents stimulate or inhibit conjugal transfer of antibiotic resistance. Therefore, this study indicates the safety
of using the plant extracts as herbal remedies in treatment of bacterial infections as they do not increase the
selective pressure that potentiate bacterial resistance. In addition, this study provides useful data that will
shed light on the use of the selected herbal extracts as alternatives to conventional anti-microbials.
5.0 Conclusion
The 27 under investigation strains were multi-drug resistant. Methanol extracts from root and barks of W.
ugandensis exhibited better anti-microbial properties than other plant extracts tested. The study established
that the MIC of methanol extracts from the root and bark of W. ugandensis against the MDR gram-negative
bacterial strains was 42.5 µg/ml. Exposure of test strains to sub-lethal extract concentrations of the effective
extracts of W .ugandensis does not induce resistance to conventional antibiotics.

Acknowledgement
This work was funded by Jomo Kenyatta University of Agriculture and Technology, Centre for Microbiology
Research (CMR), an arm of the Kenya Medical Institute (KEMRI) and the Vlaamse Interuniversitaire Raad (VLIR,
PhD grant No. BBTP2007-0009-1086).

136
References
Bekele, T. (2008). Antidiabetic activity and phytochemical screening of crude extracts of Ajuga remota. Masters
Thesis. Addis Ababa University, Ethiopia.

Brooks, C., J. W. and Draffan, G. H. (1969). Sesquiterpenoids of Warburgia species-II ugandensolide and
ugandansidial (cinnamodial). Tetrahedron. 25, pp 2887-2898.

Daniyan, S. Y. and Muhammad, H. B. ( 2008). Evaluation of the antimicrobial activities and phytochemical
properties of extracts of Tamaridus indica against some diseases causing bacteria. African Journal of
Biotechnology, 7 (14), pp 2451-2453.

Das, K., Tiwari, S. K. R. and Shrivastav, K. D. (2010). Techniques for evaluation of medicinal plant products as
antimicrobial agent: Current methods and future trends. Journal of Medicinal Plants Research. 4(2), pp 104-
111.

Gonzalez-Lamothe, R., Mitchell G., Gattuso M., Diarra S. M., Malouin, F. and Bouarab, K. (2009). Plant
antimicrobial agents and their effects on plant and human pathogens. International Journal of Molecular
Sciences. 10, pp 3400-3419.

Haraguchi, H. (1998). Mode of action of antimicrobial substances in plants. Journal of Recent
ResearchDevelopments in Agricultural and Food Chemistry. 2 (1), pp 258-268.

Jaki, B. U. Franzblau, S. G., Chadwick, L. R., Lankin, D. C., Zhang ,F., Wang Y. and Pauli G. F. (2008). Purity-
activity relationships of natural products: The case of anti-TB active ursolic acid. Journal of NaturalProducts.
71, pp 1742-1748.

Krishnaiah, P. Devkota., Etienne, T. and Norbert, S. (2007). Anthraquinones from the stem bark of
Stereospermum zenkeri with antimicrobial activity. Journal of Phytochemistry. 68(11), pp 1595-1599.

Lewis, K. and Ausubel, F. M. (2006). Prospects of plant derived antibacterials. Jouranal of Natural
Biotechnology. 24, pp 1504-1507.

Manguro, L. O. A., Ugi, I., Lemmen, P. and Hermann, R. (2005). Flavonol glycosides of Warburgia ugandensis
leaves. Journal of Phytochemistry. 64, pp 891-896.

Mascolo, N., Izzo A. A., Borrelli F., Capasso, R., Di Carlo, G., Sautebin, L. and Capasso, F. (2004). Healing powers
of aloes. In: Reynolds, T. (Editor). Aloes: The genus Aloe. CRC Press, Boca Raton, Florida, United States. pp.
209–238.

Mbwambo Z. H., Erasto P., InnocenT E. and Masimba P. J. (2009). Antimicrobial and cytotoxic activities of fresh
leaf extracts of Warburgia Ugandensis. Tanzania Journal of Health Research. 11(2).

McMahon, S. A., Blair, S. I., Moore, E. J. and McDowell, A. D. (2007). Habituation to sub-lethal concentrations
of tea tree oil (Melaleuca alternifolia) is associated with reduced susceptibility to antibiotics in human
pathogens. Journal of Antimicrobial Chemotherapy. 59, pp 125–127.

Michel, M. and Gutmann, L. (1997). Methicillin-resistant Staphylcoccus aureus and vancomycin-resistant
Enterococci: Therapeutic realities and possibilities. Lancet. 349, pp 1901–1906.

Miyasaki1, Y., Nichols1 W. S., Morgan1, M. A., Kwan1, J. A., Van Benschoten, M. M., Kittell, P. E. and Hardy1,
W. D. (2009). Screening of Herbal Extracts against Multi-Drug Resistant Acinetobacter baumannii. Jouranal of
Phytotherapy research. DOI: 10.1002/ptr.3113

Olila, D., Olwa, O. and Opuda-Asibo, J. (2001). Antibacterial and antifungal activities of extracts of Zanthoxylum
chalybeum and Warburgia ugandensis, Ugandan medicinal plants. Journal of African Health Science. 1(2), pp
66–72.
137
Raji Y, Oloyo, A. K. and Morakinyo, A. O. (2006). Effect of methanol extract of Ricinus communis on
reproduction of male rats. Asian Journal of Andrology. 8 (1), pp 115 – 121.

Somchit, M. N., Reezal, I., Nur I. E. and Mutalib, A. R. (2003). In vitro Antimicrobial Activity of Ethanol and
Water Extracts of Cassia alata. Journal of Ethnopharmacology. 84, pp 1-4.

Suffredini, I. B., Paciencia, L. B., Nepomuceno, D. C., Younes, R. N. and Varella, A. D. (2006). Antibacterial and
cytotoxic activity of Brazilian plant extracts – Clusiaceae. Mem Inst Oswaldo Cruz. 101, pp 287–290.

Tadeg H., Mohammed E., Asres K. and Gebre-Mariam T. (2005). Antimicrobial activities of some selected
traditional Ethiopian medicinal plants used in the treatment of skin disorders. Journal of Ethnopharmacology.
100, pp 168-175.

Thakurta, P., Bhowmik, P., Mukherjee, S., Hajra, T., Patra, A., Bag, P. (2009). Antibacterial, antisecretory and
antihemorrhagic activity of Azadirachta indica used to treat cholera and diarrhea in India Journal of
Ethnopharmacology. 111(3), pp 607-612.

Veen, H. W. and Konings, W. N. (2007). Drug efflux proteins in multidrug resistant bacteria. Journal of
Biological Chemistry. 378, pp 769–777.

Wube, A. A., Bucar, F., Gibbons S. and Asres, K. (2005). Sesquiterpenes from Warburgia ugandensis and their
antimycobacterial activity. Journal of Phytochemistry. 66(19), pp 2309.

138
Table 1: Plant species screened for their antimicrobial activity

Plant name Plant family Phytochemicals Medicinal uses
Clausena anisata Rutaceae Flavonoids, tannins, saponins f Stomach aches, whooping cough, malaria f

Aloe secundiflora Aloceae Phenolic compounds: chromone, Disinfectant, treatment of Pneumonia, malaria, chest pains k
anthraquinone or anthrone derivatives k
Strychnos henningsii Loganiaceae Alkaloids, saponins j Mouth antiseptic, wounds, gastrointestinal disorders, malaria j
Ajuga remota Lamiaceae Flavonoids, tannins and sterols i Bacterial infections i
Ricinus communis Euphorbiacea Alkaloids, saponins, tannins, phenolic h Stomach aches, diarrhoea, boils, burns, worms, venereal
diseases h
Zanthoxylum chalybeum Rutaceae Alkaloids and saponins g Bacterial infections, malaria, colds, cough, toothache g
Tamarindus indica Caesalpinaceae Alkaloids, flavonoids, saponins, tannins f Treatment of scabies, boils, diarrhoea, dysentery f
Warburgia ugandensis Canellaceae Sequiterpene dialdehydes: warburganal, Constipation, treatment of bacterial infections, stomach aches,
muzigadial, polygodial e coughs, muscle pains, weak joints, body pains e
Terminalia brownii Combretaceae Tannins, saponins, flavonoids, alkaloids c Diarrhoea, stomach ache, fevers, hepatitis, colds d
Azadirachta indica Maliaceae Tannins, saponins, flavonoids, terpenoids, Abdominal colic, treatment of wounds, boils, scabies, malaria,
alkaloids a rheumatism b
aKrishnaiah et al. 2008; bThakurta et al. 2009; cOsuga et al. 2006 ; dZakaria et al., 2007; eHaraguchi, 1998; fDaniyan and Muhammad, 2008; gOlila et al. 2001;
hRaji et al., 2006; iBekele, 2008; jMichel et al. 1999; kMascolo et al., 2004.
139
Table 2: Susceptibility of the 27 clinical Gram-negative strains to 15 conventional antibiotics

Test Strains
Antibiotics E 1E 2 E 3 E 4 E 5 E 6 E 7 K 1 K 2K 3K 4 K 5 K 6 K 7S 1S 2S 3S 4S 5S 6S 7P 1P 2P 3P 4 P 5 P 6
NOR S R R S S S R S R R R R S R S R S S R S S S S S S S S
SMX R R R R R R R S R R R R S R R R R R R R R R S R R S R
NA R R R R R S R S R R R R R R R S S S R S S R R S S R R
TM R S S R R R S S R R R R S R R R R R R R R R R R R R R
C R R R R R S R S S R R R R S R R R R R R R R R R R R R
N R R R R R R R S R R R R R R R R S S S S S R R S S S S
S R R R R R R R R R R R R R R R R R R R S R R R R R R S
MN R R R R S R I S S R R R R R R R R S R R R R R S R R R
CXM R R R R R R R S R S R R R R S S S S S S S S R S S R R
CFM R R R R R R R S R S R R S R S R S S S S S S R S S R R
CRO R R R R R R R S R S R R R R S R S S S R S R R S S S R
ATM R R R R R R R S R R R R S R S R S S S S R S S S S R R
FOX R S S S S S S S S S S R R S S S S R S S S R R S S R R
AUG R R R R R R R S R R R R R R R R R R R R R R R R R R R
AMP R R R R R R R R R R R R R R R R R R R R R R R R R R R

R: Resistant (intermediate phenotypes were recorded as resistant); S: Sensitive; Antibiotics: NOR: Norfloxacin;
SMX: Sulfamethoxazole; NA: Nalidixic acid; TM: Trimethoprim; C: Chloramphenical; N: Neomycin; S: Streptomycin;
MN: Minocycline; CXM: Cefuroxime; CRO: Ceftriaxone; ATM: Aztreonam; FOX: Cefoxitin; AUG: Augmentin; AMP:
Ampicilin. Gram-negative clinical isolates of the species: E. coli: E -E ; K. pneumoniae: K -K ; P. aeruginosa: P -P ; S.
1 7 1 7 1 6
typhi: S -S
1 7
140